1. Field of the Invention
The present invention relates to a light emitting device, an electric device provided with a light emitting device, and a method of producing the light emitting device. More specifically, the present invention relates to a light emitting device which can be applied to a light emitting display array or the like, and particularly to an electroluminescent light emitting device formed of an organic material. The present invention also relates to a display apparatus provided with the above light emitting device and electric devices such as a sensor device, exposure apparatus, and lighting apparatus. Furthermore, the present invention also relates to a method of producing the light emitting device.
2. Description of the Related Art
Organic electroluminescence using an organic material has various advantages over an inorganic electroluminescence. That is, organic electroluminescence devices can be realized in a flexible form, and their luminescence wavelength can be selected from a wide range. Furthermore, organic electroluminescence devices can easily be fabricated by means of a coating technique. Besides, large devices of this type can be easily produced at low cost. Another advantage is that organic electroluminescence devices can be driven by a low voltage. Consequently, there are intensive research and development activities on the organic electroluminescence.
Although electroluminescence devices have the advantage that they can emit light of various colors, it is difficult to realize a single electroluminescence device which can emit a plurality of colors. That is, it is required to form active layers into desired patterns using different materials corresponding to desired colors by means of evaporation or coating. However, very complicated production processing is required to form such a structure. Furthermore, it is difficult to realize a light emitting device in which the color of the emitted light varies from one small area to another small area.
It is also known in the art to form a plurality of light emitting layers corresponding to a plurality of desired colors. In this case, however, a complex layer structure is required. In another known technique, color filters are disposed on a single active layer which emits monochrome light. In this case, however, the color filters result in an increase in cost. Furthermore, light absorption by the color filters causes a reduction in the brightness and also causes degradation in color purity.
One known technique proposed to solve the above problems is to partially change the thickness of a transparent electrode made of ITO (indium tin oxide) so as to modify the optical path depending on the change in the thickness, thereby changing the wavelength of emitted light from one small area to another small area (The 41st Meeting of The Japanese Society of Applied Physics and Related Societies, 28P-N-16, 1994).
Although the above technique can provide means for partially changing the wavelength of emitted light within a single device, this technique has the disadvantage that the evaporation process has to be performed a plurality of times so as to control the thickness of the ITO layer. This causes an increase in complexity of the production process and also causes an increase in cost.
Furthermore, a pattern registration error occurs during a plurality of masking processes, and nonuniformity occurs in the conductivity of the ITO layer.